Personal system for the detection of a risky situation, more particularly of a fall prone situation

ABSTRACT

A method for preventing and detecting a fall of a user and implementing a system including sensors and alarm, a pair of eyeglasses with hinged stems including rims for supporting glasses, worn by the user. The sensors are set in the hinged stems and the rims of the eyeglasses. The sensors include a triaxial accelerometer, an IR transmitter and an IR receiver of infra-red light both directed to the cornea of the user, and a barometric sensor. The triaxial accelerometer signal is acquired and processed to derive a walking pace parameter, a sit to stand parameter, a head posture parameter and an acceleration magnitude over the three axes. A composite index is computed based on the walking pace, the sit to stand and the head posture parameters. The alarm is generated if the first composite index exceeds a threshold.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.16/178,365 filed Nov. 1, 2018, which claims benefit of U.S. ProvisionalApplication 62/667,515 filed May 5, 2018 and which is acontinuation-in-part of U.S. application Ser. No. 15/852,554 filed Dec.22, 2017, which is a continuation-in-part of PCT/FR2017/051362 filed May31, 2017, which claims priority from French Application 16 54922 filedMay 31, 2016, each of which are incorporated herein by reference in itsentirety.

FIELD OF THE INVENTION

The invention is about a personal system for the detection of a riskysituation and alert. The invention belongs to the field of connectedwearable devices capable of measuring physiological data of anindividual.

As nonlimiting examples, such a risky situation involves cases ofpotential reduced alertness, following or preceding drowsiness,dehydration, loss of consciousness, or a fall.

More particularly the invention relates to connected eyeglassesfeaturing sensors for assessing the physiological state of anindividual, with regard to specific risky situations, before saidindividual may feel any alerting symptom.

BACKGROUND OF THE INVENTION

Even a light fall, may potentially be a vital hazard when it affects anelderly or a disabled person.

Yet, the harmful consequences of a fall, even heavy, are mitigated ifassistance is provided to the person in a short period of time. Othercomparable cases concern, for example, seizures.

Falls are the leading cause of death in people over 65. Every second ofevery day in the United States an elderly falls, making falls the numberone cause of injuries and deaths from injury among older Americans. In2014 alone, older Americans experienced 29 million falls causing sevenmillion injuries and costing an estimated $31 billion in annual Medicarecosts.

Besides death cases, people who are victims of a fall usually experiencea loss of autonomy and a loss of self-confidence that also haveimportant consequences. Studies show that, in the case of an elderlyperson, the longer the time spent on the ground after a fall, the moreserious the consequences.

OBJECT AND SUMMARY OF THE INVENTION

It is therefore an objective of the invention to be able to detect thefall of a individual, more particularly for older adults, especiallyduring time when there is no one around to help, in order to call forrescue as quick as possible when potentially required.

It is also an objective of the invention to provide means for detectinga fall prone situation, that is detecting the physiological state of anindividual that may lead to a fall, before the fall actually takesplace.

Alertness disorder is an example of a situation that may lead to a fall,it may be the result of, e.g., an extreme fatigue, or more commonly, forelderly, the result of dehydration, drugs or alcohol consumption. Thus,in some instances, the detection of a loss of alertness and the warningof the person experiencing it, or of one of his relatives, may prevent afall or mitigate its aftermath.

Dehydration, drowsiness and fall are connected together in manyinstances. Dehydration may cause dizziness and a loss or alertness, evena loss of consciousness leading ultimately to a fall. Dehydration isinfluenced by alcohol and drugs consumption, therefore an earlydetection of dehydration may in some instances prevent a further risk ofloss of alertness. An early detection of a drop of alertness may preventa fall. The severity of a fall, and the capability of the victim torecover herself from the fall may be assessed by measuring the alertnessof the person after the fall.

Up to 30% of seniors aged 65 and above, who are admitted to the hospitalare dehydrated, in 1.5% of the cases, dehydration is the primary causefor hospital admission.

Physiological measurements performed on groups of individuals inlaboratory conditions can statistically detect signs of reducedalertness, sleep, fall, loss of consciousness or dehydration. Thesetests use multiple sensors that can be worn by an individual only inlaboratory conditions. When the results of these experiments are usedwith the aim of developing a personal detection device, the detectionquality usually drops, for various reasons, including:

-   -   it is difficult to integrate suitable sensory, in terms of the        number of sensors and their reliability of measurement, in a        wearable device;    -   the wearable device is unsightly, uncomfortable, too intrusive        or too perceived by the individual and his relatives as a        surveillance device, so that the individual does not wear it;    -   the detection reliability is not satisfactory, because of the        reduced number of sensors and, because it is based on        statistical data not adapted to the individual itself and his        way of life, leads to the generation of false alarms, so that,        losing its confidence in the device, the user does not wear it        anymore;    -   the detection is too late, for instance, detecting an actual        fall may be life-saving for the victim by alerting rescue on        time but an earlier detection of a potential fall prone        situation may help the person prevents the fall and its harmful        effects by herself;    -   the detection system usually uses cascading tests where the        outcome of a first test determines the implementation of a        second test, etc. when reliability is poor it only gets worse        from one test to the other and generates positives false or        negatives false; and    -   the autonomy of the personal system is low because of the power        consumption of the many components and of the required computing        power.

While detecting a fall, a loss of alertness and a dehydration state mayprevent many hazardous situations, there is a need for a broader fallprone situation detection that may or may not be combined with the riskysituation detection as disclose in U.S. Pat. No. 10,964,190.

The invention pertains to a system based on an aesthetic sensor,autonomous and lightweight, specifically suited to its user.

The system and the method of the invention use a limited number ofsensors, thus limiting the power consumption, but are capable ofdetecting a fall prone situation, an actual fall and an after-fallrecovery.

Although the system is more particularly intended to the elderly, it isrelevant to any individual, comprising healthy individuals.

To this end, the invention pertains to a method for preventing anddetecting a fall of an individual and implementing a system comprising:

a pair of eyeglasses with hinged stems including rims for supportingglasses, worn by the individual and comprising a plurality of sensorsand an alarm, the plurality of sensors being set in the hinged stems andthe rims of the eyeglasses comprising:

-   -   a triaxial accelerometer;    -   an IR transmitter and an IR receiver of infra-red light both        directed to the cornea of the user;    -   a barometric sensor;

wherein each sensor of the plurality of sensors is generating a signal,and is connected to a microprocessor configured to execute a computerprogram stored in a memory to collect and analyze data issued by theplurality of sensors, and to trigger alarms in response to an analysisof the data; and

wherein the triaxial accelerometer signal is acquired and processed inorder to derive form it a walking pace parameter, a sit to standparameter, a head posture parameter and an acceleration magnitude overits three axes.

The method comprising the steps of:

computing a first composite index based on the walking pace, the sit tostand and the head posture parameters; and

generating a first type of alarm if the first composite exceeds athreshold. The sensors, thus arranged at the level of the head of theindividual wearing the pair of eyeglasses allow not only to detect afall but to detect a fall prone situation and to warn the individual orthe caretakers when such a situation arises before the fall occurs.

By using at least two parameters for each kind of detection, each beingderived from the detection of at least one pattern in the signal issuedby at least one sensor, and combining them into a composite index, therobustness of the system is improved with regard to false alarms, eitherpositive or negative, and can be tuned to be adapted to the individualwearing it.

The system may also comprise additional sensors according to specificembodiments. However, the use of a small number of sensors for thedetection of a complex situation by a smart processing of the signal,allows a reduced power consumption and a broad operation autonomy, whilemaintaining a light weight for wearing comfort.

The installation of such sensors in a pair of classic eyeglasses, withfoldable stems, enables the individual to wear the device in a discreetand aesthetic way. As compared to other personal systems of detection,such as wristbands or medallions, the installation of sensors in a pairof eyeglasses favors a nearly continuous wearing of said sensors by theuser during its hours of activity, most of users being used to weartheir eyeglasses as soon as they wake up.

The composite index may be computed from more than two parameters butuses at least two parameters derived from the signals issued by thesensors and collected by the processing and calculation unit.

Depending on of the risk to be detected and assessed, the two parametersare either derived from the signal issued by the same sensor or from thesignals issued by two different sensors.

Advantageously, one of the two parameters is relevant in the context ofreferences specific to the individual wearing the eyeglasses and thesecond parameter is relevant regardless of the individual.

Usually, but not necessarily, the first parameter is indicative of anearly stage of the risk while the second parameter is indicative of amore advanced stage of risk. Therefore, the combination of bothinformation in the composite index allows said composite index to beadapted to the individual, by a preliminary measurement and/or through amachine learning mechanism, while the taking into account of the secondparameter provides a safety net in case of a hard issue.

Therefore, the accuracy and the reliability of the detection and of thetrigger of a given alarm level are improved.

Throughout the text the term ‘or’ must be interpreted as inclusive(and/or).

The invention is advantageously implemented according to embodiments andvariants exposed hereunder, which are to be considered individually orin any technically operative combination.

The method uses the same set of sensors to detect a fall, whether softor hard, of the individual and to this end comprises the steps of:

-   -   acquiring a signal of the barometric sensor;    -   computing a second composite index based on:    -   an acceleration magnitude combined along three axes of the        triaxial accelerometer;    -   a variance of the acceleration magnitude over a predetermined        duration;    -   an acceleration component over an axis of the three axes of the        triaxial accelerometer parallel to gravity;    -   the acceleration magnitude combined over the three axes of the        triaxial accelerometer in a plane perpendicular to the gravity;    -   a variation of a barometric pressure between two moments; and    -   generating a second type of alarm corresponding to the detection        of a fall if the second composite index exceeds a threshold.

Furthermore, once a fall is detected the method uses the same set ofsensors to assess the recovery of the fallen individual, and to this endcomprises the steps of:

-   -   controlling the IR transmitter, collecting and processing a        signal from the IR receiver;    -   processing the signal of the IR receiver for detecting a closure        and an opening of an eyelid of the individual;    -   computing an alertness composite index based on the opening and        closure events of the eyelid;

when a second type of alarm is generated:

-   -   computing a third composite index based on:        -   a body posture parameter derived from the head posture            parameter and the barometric sensor; and        -   the alertness composite index; and

generating a third type of alarm when the third composite index exceedsa threshold.

Advantageously, the method of the invention comprises a step ofcontrolling that the eyeglasses are worn by the individual by performinga check out test that comprises the steps of activating the IRtransmitter and analyzing the IR receiver signal in response.

According to a preferred embodiment, the computation of the walking paceparameter comprises:

-   -   projecting the signals issued by the triaxial accelerometer on        an axis parallel to the gravity direction to obtain a pedometer        signal;    -   obtaining a threshold value and detecting consecutive peaks in        the pedometer signal exceeding the threshold, during a given        assessment time;    -   measuring the time separating 2 consecutive peaks during the        measuring time;    -   computing the variance of this time over the assessment time;        and    -   using this parameter as part of the first composite index.

According to this embodiment, the method further comprises the steps of:

-   -   assessing an angle of the head posture variation of the        individual during the assessment time;    -   obtaining a threshold angle and measuring the time the angle        exceeds this threshold during the measuring time; and    -   using this parameter as part of the first composite index.

Further parameters are computed based on the sit to stand movements ofthe individual.

According to an exemplary embodiment, the method of the inventionfurther comprises the steps of:

-   -   detecting a sit to stand event by a specific pattern in the        signals issued by the sensor comprising an acceleration parallel        to the gravity axis;    -   measuring the duration of the sit to stand event;    -   measuring the peak acceleration during the sit to stand event;        and    -   using these parameters as part of the first composite index.

Advantageously, the method further comprises:

-   -   counting the number of sit to stand events per day; and    -   using this parameter as part of the first composite index.

DESCRIPTION OF THE DRAWINGS

The invention is described hereunder according to its preferredembodiments, in no way limiting, and with reference to FIGS. 1 to 18, inwhich:

FIG. 1 is a perspective view of an exemplary embodiment of theeyeglasses of the system of the invention;

FIG. 2 shows in a perspective view, an exemplary embodiment of thearrangement of electronics within the frame of the eyeglasses of thesystem the invention;

FIG. 3 shows, according to a partial exploded view in perspective, anexemplary embodiment of the hinge of the stems of the eyeglasses of thesystem according to the invention;

FIG. 4 is a scheme showing an exemplary embodiment of the system of theinvention in its so-called connected version;

FIG. 5 is a flow chart of an example of signal processing leading to thegeneration of an alarm;

FIG. 6 shows, according to a perspective view, the operation of thetransmitter and the receiver of the system of the invention, with theeye open in FIG. 6A and with a closed eye in FIG. 6B;

FIG. 7 represents an example of an eye-tracking chart derived from theinfra-red receiver signal;

FIG. 8 shows the time evolution of the magnitude of the signal issued bythe IR receiver as well as its derivative during a spontaneous eyeblink;

FIG. 9 represents the evolution of the AVR parameter with time, FIG. 9Afor an awakened person, and FIG. 9A in the case of a drowsy person;

FIG. 10 shows an example of the evolution of the acceleration measuredaccording to the direction of gravity during a head drop;

FIG. 11 is a flow chart of an exemplary signals processing and alarmtriggering according to the method of the invention;

FIG. 12 shows the evolution of the signal issued by the IR receiverduring wearing and take off of the eyeglasses of the system of theinvention, in FIG. 12A the raw signal, and in FIG. 12B, the filteredsignal and its time derivative;

FIG. 13 shows examples of evolution of signals during a fall event, FIG.13A the signal issued by the accelerometer, FIG. 13B the signal issuedby the barometric sensor;

FIG. 14 shows an example of the evolution of the acceleration in a planeperpendicular to gravity during a soft fall event;

FIG. 15 shows, according to a perspective view, an exemplary embodimentof the arrangement of additional sensors in an enhanced version of theeyeglasses of the system of the invention;

FIG. 16 shows an example of the evolution with time of an accelerationsignal on an axis parallel to the gravity direction during a walkingsequence;

FIG. 17 shows a signal giving the evolution of a head posture during awalking sequence; and

FIG. 18 shows an exemplary evolution with time of an acceleration signalparallel to the gravity axis featuring sit to stand events.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1, according to an exemplary embodiment, sensors of the system ofthe invention are borne by a pair of spectacles (100), featuring twohinged stems (110), two rims (120) holding prescription or not lenses,said rims (120) being linked by a bridge (130) resting on the nose ofthe user when the spectacles are worn. According to this exemplaryembodiment, the stems comprise two parts. A first part (111), so-calledfront part, extends from the stem hinge (140) along about half of thestem length. The second part (112) of the stem, so-called aft part, isconnected to the first part (111) e.g., by clipping. This second partrests on the ear of the user, and include or not a curved temple tip,also called earpiece, pursuant to different styles of eyeglasses.

According to this exemplary embodiment, the front part of the stem bearselectronic modules, while the second part (112), or aft part, does notinclude any electronics. Therefore, this second part is adapted to themorphology of a user like for any conventional eyeglasses, by using ashorter or a longer second part (112), or even by distorting it byheating. Similarly, the rims comprise two parts, the outer part (121) ofthe rims, extending substantially between the hinge and the basis of therims, bears sensors, including an IR transmitter (151) and an IRreceiver (152). The lower part and the inner part of the rims (120), upto the bridge (130), are free from any electronics and eases themounting of any type of lens.

According to this exemplary embodiment, the rims are made of plastic andfully surround the lenses. As a for instance, the lenses are set up inthe spectacles by heating the lower part of the rims and theirconnections to the bridge. However, the design of the spectacles of thesystem of the invention authorizes the use of other types of rimsbetween the outer part (121) and the bridge (130), such as metallic rimsor wire type rims. According to this exemplary embodiment the nose-padsare integrated to the rims and the bridge.

However, the design of the spectacles, in the same way that it allowsthe fitting of other types of rims, also allows the set-up of nose-padshinged on pad arms, which then can be adjusted in the same way as forconventional eyeglasses. Therefore, the spectacles of the system of theinvention are adaptable to the morphology of their user, likeconventional eyeglasses, to achieve optimal wearing comfort andstability.

The eyeglasses are therefore suited to any type of lenses, prescriptionor not, simple, bifocals or progressive, or simply fashionable. Theyallow, in addition, different variations of style to match theiraesthetic with the taste of the user. The mounting of the lenses as wellas the mechanical adjustments of the eyeglasses of the system of theinvention are preferentially performed by a professional, e.g., anoptician, according to known techniques, similar to the techniques usedfor conventional eyeglasses.

Electronic modules are distributed between the front (111) parts of theleft and the right stems and are connected by a flexible bus runningthrough the upper parts of the rims and the bridge (130).

FIG. 2, according to an exemplary embodiment, the eyeglasses of thesystem of the invention comprise several circuit boards (211, 212, 221,222), on which the various sensors, acquisition and calculation means aswell as data transmitting means, are welded or snapped.

According to this exemplary embodiment, the electronic boards are housedinside the front part of the stems and inside of the outer parts of therims. As a for instance, those parts of the stems and rims are made of aplastic material such as a polyamide or acetate or of a compositematerial comprising a thermosetting or thermoplastic matrix reinforcedby a fibrous charge of glass, of carbon or of natural fibers such asbamboo or linen, for more lightweight and strength.

These envelopes provide both mechanical shielding and weatherproof ofthe electronics, and are available in different colors, differentsurface textures and different shapes.

The electronic boards (211, 212, 221, 222) are connected to each otherby flexible buses (241, 242, 230), comprising a central bus (230)extending between the right side and the left side of the spectacles andrunning through the inside of the upper parts of the rims and thebridge, and side buses (241, 242) connecting the boards (211, 212)located inside the front parts of the stems and the boards (221, 222)located inside the outer edges of the rims. The side buses (241, 242)are running through the hinges (140) of the stems, said hinges beingspecifically designed for this purpose.

Thus, the functions of measurement, signal processing, calculation, datatransmission and power distribution are essentially distributed betweenthe two stems, so as to balance the weight distribution between the twosides of the eyeglasses frame.

The sensors used are of the ultra-miniaturized type also known as “MEMS”or “NEMS”.

According to one embodiment, the eyeglasses comprise an IR transmitter(151) and an IR receiver (152), set on an electronic board (222) withinthe outer edge of a rim. The transmitter and the receiver are orientedtowards the eye of the user.

In another embodiment, the same layout is set in both the left rim andthe right rim. Doubling of the device allows for measurements on eacheye in order to assess the consistency of the obtained signals, and toonly use the signals issued by one of the transmitter-receiver couple,in the case of malfunction of the other.

These sets of IR sensors (transmitter and receiver) are used to measureeye blink frequencies and eyes closure in order to assess the level ofalertness of the person wearing the glasses.

They may also be used to measure the IR light absorption of the bloodconveyed by the blood vessels in the eye, either under the sclera or inthe eyelid. The pattern of absorption of IR light by the blood can becorrelated to the hydration state of the person.

To this end, the emission power of the IR receiver is increased atregular time intervals, for instance, every 10 minutes, in order tomeasure the IR absorption pattern of the blood and assess thedehydration state of the person.

The reflectance of the eye is also a function of the hydration of theeye, which in turn is an indicator of the dehydration state of theperson. This reflectance may also be measured by means of the IRtransmitter and the IR receiver.

These parameters: IR absorption pattern of the blood and reflectancechange from one person to another, therefore a calibration or anadaptation are required for deriving a parameter and a severity indexbased on these measurements.

Additionally, the dehydration state of the person may also be measuredthrough the voltage response of the skin impedance circuit. Thisparameter is less sensitive to the individual as compared to the formerones.

To this end, the eyeglasses of the invention may comprise two electrodesmade e.g., of copper that are here shown as circular electrodes, but cantake any other suitable shape, such as strips.

A low voltage sine wave generator, as for instance producing a 3 voltssine wave at 50 kHz, is connected to one electrode (161) and thealternative current is transmitted to the other electrode (162) by theskin, thus allowing to measure the impedance of the skin by inserting asensor in the circuit.

The electrodes are set on the front part of a stem in such a way thatthey contact the skin of the user wearing the eyeglasses.

The impedance variation of the skin at such a frequency results fromresistance and capacitance variation with the hydration level. Theimpedance measurement is in the range of a few hundreds of ohms, e.g.,200 to 500 ohms.

The value corresponding to a well hydrated subject can be calibrated andstored in the memory means of the device.

In an alternative embodiment, impedance measurements may be performed atvarious frequencies of the supplied current alternative current.Capacitance variations are more sensitive in the lower frequency range,i.e., in the kHz range, while resistivity influences the results in the10 kHz range.

A drop of about 10% from the nominal value of the impedance thusmeasured, indicates a dehydration state.

Such measurements may be performed on regular time intervals, e.g.,every 30 minutes.

A triaxial accelerometer (251) is set on one of the electronic boardsincluded in the stems, i.e., on the electronic board (211) located inthe right stem according to the exemplary embodiment shown in FIG. 2.The accelerometer measures accelerations in three directions (x, y, z).

According to this nonlimiting example, said accelerometer is mounted sothat the acceleration of gravity is oriented pursuant to the positive yaxis when the eyeglasses are worn by the user, that is to say,substantially parallel to the direction of the gravity if the user isstanding and looking straight in front.

According to another embodiment, the accelerometer sensor is included ina so-called inertial MEMS, comprising a triaxial accelerometer and agyro sensor. According to yet another embodiment, the accelerometer isincluded in a MEMS, comprising a triaxial accelerometer, a gyro sensorand a magnetic compass.

Advantageously, the sensor comprising the accelerometer includes anintegrated temperature probe, making it possible to correct the signalgain and linearity according to the sensor temperature.

As a nonlimiting example, the accelerometer has an amplitude ofmeasurement of ±6 g (±58.86 ms⁻²) on each axis.

According to a specific embodiment, a second triaxial accelerometer (notshown) is set on the electronic board (212) of the left stem of theeyeglasses. The combination of the two accelerometers signals allows toimprove the accuracy of the measurement of rotational head movements andto better differentiate these movements from movements of the whole bodyof the user.

The second accelerometer is preferably set on the other stem in symmetrywith the first one. Head movements, like flexion-extension (movement ofthe “yes” head sign), axial rotation (movement of the “no” head sign),or of side inclination, in the accelerations projecting in opposed signson the axes of the two accelerometers.

Thus, for example, while referring to the (x, y, z) system of FIG. 2, aside inclination results in opposite projections of the acceleration onaxes y and z of the two accelerometers.

An axial rotation of the head results in opposite projections of theacceleration according to axes x and z of the two accelerometers. Thecombination of this information with information from the gyro sensorand the magnetic compass, in an embodiment featuring these types ofsensors, allows to detect complex posture changes of the user.

A barometric sensor (252) is set on an electronic board (211), accordingto this example on the electronic board located in the right stem, butalternatively on the electronic board (212) located in the left stem.Such a MEMS sensor can commonly detect a pressure variation of about 6Pa, which corresponds to a variation of altitude of approximately 20inches (50 cm). Processing the signal of such a barometric sensor,allows for example to detect a position change of the user, e.g., from astanding position to a sitting or lying position, and vice versa, whensaid user wears the eyeglasses of the system of the invention.

The risky situations whose detection may be performed; loss ofalertness, dehydration, fall prone situation, fall, and fall recovery,are detected by combining information issued from the processed signalsof:

-   -   the IR receiver (152), excited by the IR transmitter (151);    -   the triaxial accelerometer (251);    -   the barometric sensor (252); and    -   the skin impedance measurement through the electrodes (161,        162).

The detection reliability is improved by adding to these sensors:

-   -   a second IR transmitter and receiver couple;    -   a second triaxial accelerometer mounted symmetrically to the        first on the other stem of the eyeglasses; and    -   a second pair of electrodes either on the same stem but located        in a different area, or on the other stem, the second pair of        electrodes being of a different shape.

In this embodiment one pair of electrodes may be supplied by analternative current in the 1 kHz-9 kHz range, while the other pair ofelectrodes is supplied by an alternative current in the 10 kHz-90 kHzrange.

The detection reliability is further improved, as well as the capabilityof discriminating more finely some situations, by adding to the previoussensors:

-   -   a gyro sensor; and    -   a magnetic compass.

These lasts two sensors, are advantageously integrated, alone or incombination, in a MEMS also comprising a triaxial accelerometer.

More specifically a fall prone situation is detected by combining theinformation issued by the processed signals of:

-   -   the triaxial accelerometer    -   the barometric sensor

A fall is detected by combining the information issued by the samesensors but with a different processing.

Therefore, these two sensors are the only one required, if the purposeof the eyeglasses is limited to fall prevention, which allow to makeeconomic eyeglasses with a very low power consumption for such aspecific application.

Adding the IR emitter and receiver allows to improve the relevance ofthe alarm generation by reducing negative and positive false, and alsoadds the capabilities of after fall recovery assessment and of alertnessassessment.

Therefore, starting from the same base, the pair of eyeglasses may becustomized for various applications, either by adding or by removingsensors or by uploading a specific software implementing a specificmethod and using part or all of the sensors and the information theyissue. The processing and calculation unit is advantageously distributedbetween two modules (261, 262) set respectively on the electronic boardsof the right stem and the left stem.

As a nonrestrictive example, the module (261) of the right stemcomprises a microprocessor and memory means, including a program foracquiring the signals from the sensors, and for processing signals andcalculating the relevant parameters, whereas the module (262) of theleft stem, collects the signals of the sensors placed on this same stemand their transmission towards the module of the right stem, manages thepower supply, including the current supply to the electrodes ifimplemented, the charge of the battery (270) and the communications,whether wired or wireless with other devices, in particular towards asmartphone, a computer, or a WiFi® gateway.

The eyeglasses finally comprise means of alarm distributed between thestems, for example a colored led (282) and a buzzer (281).

According to an embodiment a miniaturized connector (not represented),for example of the micro-USB type is integrated in one the stems andallows data exchange with other devices, via a wire connection, and therecharging of the battery (270).

In a specific embodiment the module (261) comprising the microprocessoralso comprises a geolocation chip.

By using a limited number of sensors and highly integrated electronics,the weight of the eyeglasses is kept under 1.4 oz (40 grams) without thelenses, with an operating autonomy of at least 8 hours per batterycharge.

Advantageously, the eyeglasses of the system comprise foldable stems, inorder to be used, carried and tidy up like any conventional eyeglasses,more particularly to allow their tidy up in a case in order to protectthe lenses when the user is not wearing said eyeglasses.

The distribution of the electronic modules between the right stem andthe left stem, implies that a bus connects the electronic boards of thetwo stems and runs through the hinges of the stems. For this purpose,the eyeglasses of the system of the invention feature specific hingesguiding the bus during the folding and unfolding of the stems so that itfollows a high enough radius of curvature avoiding any damage to saidbus.

FIG. 3, an exemplary embodiment of the right stem hinge of theeyeglasses of the invention is shown in a position corresponding to theunfolded stem. The stem is supported by a shouldered bearing surface(340) at the end of the rim, making its precise vertical positioningaccording to the hinge rotation axis (300). The joint is performedbetween a hub (342) connected to the stem and an axle (341) housed inthe fixed part of the frame forming the aforementioned bearing surface(340).

The axle (341) comprises two parts connected to each other, the firstpart (3411) is fitted in a bore (3401) of complementary shape, made in afixed part of the frame, and the second part (3412), of smallerdiameter, around which the hub (342) revolves. The first part of theaxle is indexed in rotation in the bore, for example, by means of atenon and mortise assembly and fixed, for example, by clipping orgluing.

The bus (241) is running in the stem and goes down in the bore (3401)receiving the axle (341) by a shoulder to reach the rim. For thispurpose, the first part (3411) of the axle comprises a slit (3413) as apassageway for the bus (241). This first part (3411) of the axle extendson approximately ¾ of a circle the open part providing a clearance equalor slightly higher than 90° for the movement of bus (341) in the bore(3401) when folding and unfolding of the stems.

The hub (342) is set up in the stem, and also comprises a slit (3423),as a passageway of the bus part (241) located in the stem behind theshoulder (345), the aforementioned slit (3423) being appreciablydiametrically opposed to the slit (3413) of the axle when the stem isunfolded.

The aforementioned hub is snapped in a bore of complementary shape, inthe stem, indexed in rotation relative to said stem, for example bymeans of a tenon and mortise assembly, and fixed in said bore, forinstance by clipping or gluing.

During the folding of the stem, the part of the bus (241) entering theslit (3413) of the axle does not move, only the part in the slit (3423)of the hub does, up to the bus shoulder (345). The second part (3412) ofthe axle comprises a portion (3415) of lower diameter than the diameterof the portion guiding the pivot join, the shoulder (345) of the busglides on this portion of lower diameter during the pivoting of thestem. Thus, the radius of this lower diameter portion defines the radiusof curvature imposed on the bus (241) when folding and unfolding thestems.

The whole assembly is held in position by a rivet (343).

Advantageously, an indexing mechanism is included in the tenon of theaxle that stops the axle in rotation in the bore (3401). The hubcomprises a tenon (3425) cooperating with this indexing mechanism toindex the stem in the unfolded position and to avoid any damaging of thebus (241) by too important an aperture, because the location of the IRreceiver (152) does not make it possible to limit this angulardisplacement by an abutment of the stem on the rim, as that is usuallycarried out for conventional spectacles.

According to an exemplary embodiment, the eyeglasses of the system ofthe invention operate in a completely autonomous way, by determining theparameters related to a given risky situation and by generating alarmstowards its own means, from an analysis of these parameters performed bythe microprogram stored in the processing and calculation unit.

FIG. 4, according to another embodiment of the system of the invention,the eyeglasses (100) are said connected, and have the ability tocommunicate either permanently or periodically with another object (400)by a connection (491) either wireless, e.g., of the Bluetooth® lowenergy or Zigbee® types, or by wire.

As of some examples, the connected object (400) is a smartphone, apersonal computer or a WiFi® gateway. This object (400) is in turnconnected to one or more networks, and to other objects (401) or servers(411, 412), for example via internet (490), a cellular network (492) ora proximity wireless link (493) like a Bluetooth® link.

This embodiment makes it possible to increase the functionalities of thesystem. Thus, the connected object (400) is able to download an updateof the microprogram from an update server (412) and to upload saidupdate in the processing and calculation unit of the eyeglasses oncepaired with it.

The aforementioned connected object advantageously comprises its ownmeans of calculation and a specific program allowing an analysis of thedata collected from the memory means of the eyeglasses, then, byanalyzing these data, adjusts the eyeglasses operation according to theuser, in particular the thresholds of alarms triggering, or thecalculation parameters of these thresholds.

The same program comprised in the connected object (400) is also able toconduct tests aiming at checking the correct operation of the connectedglasses or detecting and fixing malfunctions.

For example, when the eyeglasses are comprising two couples of IRtransmitter-receiver on each rim, if an abnormal or suspect operation ofone of the couples is detected, the assessment of alertness is thenbased on the sole signals issued by the couple operating correctly. Thesame applies when the pair of eyeglasses comprise two or more sets oftwo electrodes.

According to a specific embodiment, the connected object (400) is alsocapable of transmitting alarms to third parties, through variousconnection routes, such as Internet, a proximity network or a cellularnetwork.

As a for instance, in the case of a serious fall detection, it sends analert to a rescue center (420), along with the geolocation of the personwearing the eyeglasses. According to another example of implementation,the connected object (400) sends an alert of reduced alertness of thewearer of the eyeglasses to the smartphones (401) of people in itsvicinity. Therefore, the passengers of a vehicle driven by the user arewarned about its condition and urge him to stop driving.

According to yet another example, the drop of alertness alarm is sent,for example, via a cell phone network or a DECT network, to the remotesupervisor of an operator driving a machine or an industrial gear andwearing the eyeglasses.

In still another embodiment, the information of a detected event such asa drop of alertness or a fall, of substantial severity, is sent to anassistance center, via the internet or via a cell phone network, alongwith the geolocation of the device. This geolocation can either beretrieved directly from the eyeglasses if they are equipped with ageolocation chip, or from the connected object (400) such as asmartphone, paired with the eyeglasses.

Upon receipt of this information, the assistance center may enter incontact with the user, e.g., through the smartphone (400), either by avoice or a text communication in order to check out the condition of theuser, or to help him staying alert for a limited duration, and guide himto the nearest place to stop and have a rest.

Accordingly, the eyeglasses (100) are associated with a single number ofidentification (UUID) and, through an application set up in theconnected object, to information relating to the user, such as its age,its possible pathologies, or information derived from the dataacquisition carried out by the eyeglasses, such as its average frequencyof spontaneous eye blinking.

This information, combined with data from the measurements carried outby the eyeglasses, is transmitted periodically, for example once a day,and in an anonymous way to a server (411) collecting whole of thesedata.

Therefore, this server gradually builds a large database, on whichstatistical studies implementing artificial intelligence, commonlyreferred to as the “Big Data”, are carried out and used to improve thesystem and to offer custom updates.

Accordingly, the system implements a machine learning process and adaptsspecifically to its user. This adaptation comprises two levels. A firstlevel is achieved at the level of the device itself, i.e., theeyeglasses, by implementing its own means of calculation and allows toadapt the conditions of alarm to the own characteristics of the userwithout changing the processing algorithms. A second level is reachedthrough population analysis and helps to refine the algorithms bydetection category and phenotype. This second level is implemented in aremote server (411).

FIG. 5, according to an exemplary embodiment the generation of an alarmpertaining to a given risky situation, takes into account the signals(501, 502) issued from one or more sensors. The signal issued by eachsensor undergoes a filtering step (511, 512) that is specific to eachtype of sensor in order eliminate the noise and irrelevant influences.

During a processing step (521, 522) a series of parameters (5211, 5212,5221, 5222) is extracted from each signal. These parameters are combinedduring a calculation step (530) in order to define a composite index(531) relating to the kind of monitored situation.

This composite index (531) is then compared (540) with a reference (550)stored in memory, and if it differs from this reference by a significantlevel, an alarm is generated (560).

The steps of processing (521, 522), calculation (530) and comparison(540) implement constants that are stored in the memory means of theprocessing and calculation unit. Several of these constants are specificto the wearer of the eyeglasses. Therefore, in parallel to theprocessing of alarms, in the course of a learning step (570), signalsand parameters calculated at the processing step (521, 522) areanalyzed, and the constants used for processing, calculation andcomparison may be changed by an authorized magnitude, in order to adaptto the individual wearing the eyeglasses, this method corresponding tothe first level of machine learning and customization of the system.

FIG. 6, the alertness measurement and the related generation of alarmsis essentially based on the analysis of the spontaneous eye blinkssupplemented by the detection of a head drop. The measurement of eyelidblinks is carried out from the signal issued by the IR receiver.

FIG. 6A, when the eye is open, the beam of incident light (651)generated by the IR transmitter is reflected in a light spot (650) onthe cornea, the IR receiver measures the intensity of the reflected beam(652).

FIG. 6B, when the eye closes, the incident beam (651) is reflected onthe eyelid. The reflectance of the eyelid being different from that ofthe cornea, the light intensity of the reflected beam (652) isdifferent.

Thus, the intensity of the reflected signal (652) varies according tothe eyelid surface lighted by the bright spot of the incident beam(651). The reflectance of the eyelid is higher than that of the cornea,so the more the eyelid closes the higher the intensity of the reflectedsignal (652) thus measured by the IR receiver.

FIG. 7 shows an example of the intensity (702) of the signal perceivedby the IR receiver vs time (701). Each peak reflects a more or lesscomplete closing of the eyelid. This exemplary diagram makes it possibleto distinguish the palpebral movements corresponding to voluntary eyeblinks, corresponding to higher intensity peaks, and more numerouspeaks, of lower intensity, corresponding to spontaneous eye blinks.

Spontaneous eye blinks are fast movements of the eyelid, that a personis not aware of and whose physiological role is to avoid the desiccationof the surface of the eye by ensuring the collection and the excretionof the tears and the spread out of the lachrymal film.

These movements occur according to a variable frequency depending on theindividual, of about 20 blinks per minute. The frequency and the speedof these blinks are influenced by factors such as the emotional stress,tiredness or the consumption of psychotropic substances, and accordinglyconstitute indicators adapted to the measurement of alertness.

Therefore, for the alertness analysis, only the peaks whose intensity islower than a threshold (730) is considered. This threshold is set for agiven individual, during an adjustment and calibration step of theeyeglasses.

According to a specific embodiment, voluntary eye blinks or winks, canbe used to control functions, including functionalities of the objectconnected to the eyeglasses. When implementing such a possibility, onlythe peaks whose intensity is higher than an intensity threshold (730)and of a duration longer than a given time lapse are considered.

FIG. 8, at the scale of a spontaneous eye blink, the analysis of thesignal (802) issued by the IR receiver and of its time derivative (803),allows to define several parameters, such as:

-   -   the blinking duration (811) measured by the peak full width at        half maximum or more specifically at the half of its maximum        measured intensity;    -   the duration of closure at more than 80% of the eyelid (812);        and    -   the maximum closing speed (813).

Analyzing several peaks over a given time further gives access to:

-   -   the spontaneous blinking frequency, or more precisely the number        of spontaneous blinking on a given time; and    -   the relative amount of time spent with the eyelid closed at more        than 80%.

The beginning of a peak is easily detected on the time derivative of thesignal.

The derivation operation is however affected by the noise in the signal.

To this end, the signal from the IR receiver, is first filtered in orderto eliminate the influence of ambient light, whether natural orartificial.

The part of the spectrum of the ambient light falling in the measurementrange of the IR receiver affects the response of the sensor by addingnoise and additional variation frequencies.

According to an exemplary embodiment, the influence of ambient light isthus eliminated from the signal by applying to this one a moving averagepolynomial filter, e.g., of the Savitsky-Golay type, followed by afiltering of the signal thus smoothed by a Butterworth's band passfilter, with a 10 Hz bandwidth, centered on the average frequency ofspontaneous eye blinking.

The different stages of drowsiness are characterized by an increase inthe relative time when the eyelids are closed over a given interpolationtime, because of the increase in the eye blink frequency or theincreased duration of each eye blink.

This feature is captured by the ratio of the total time spent with theeyelid closed at more than 80% (812) over an interpolation duration,further referred as PERCLOS₈₀.

According to an exemplary embodiment, this parameter is calculated overon interpolation duration of 20 seconds. For an alert individual thisparameter is less than 3%. The increase of this ratio indicates theonset of drowsiness and the decrease of alertness. This 3% level isindependent of the individual and so enables to reliably characterize afully alert state of said individual, and to calculate for this stateother parameters that better characterize the drowsiness state but areindividual dependent.

The analysis of the decrease of alertness performed over a sample ofpeople translates in an increase of the spontaneous eye blink frequencyand in an increase of the dispersion of the interval of time between 2eye blinks, in particular, because the duration of certain eye blinkslengthens.

The eye blinking frequency, and the time between two eye blinks, can beextracted from the IR receiver signal over a given interpolation time.However, if this parameter is statistically relevant over a sample ofindividuals, it is difficult to draw an actual early indicator ofreduced alertness for a given individual because the behavior changesfrom one individual to another. Therefore, such an indicator can bereliably used only for detecting an advanced state of drowsiness, closeto a slumber.

For this purpose, an indicator is calculated by considering theproportion of eye blinks having a duration of eye lid closure greaterthan a given value.

As a for instance, this threshold level is set at 0.3 seconds, and iffor 10 successive peaks of eye blinks more than 6 have a duration (811),measured by the width of the eye blink peak, longer than this threshold,then the indicator takes the scalar value of 0.6 ( 6/10).

This 0.3 second duration and this proportion of 0.6 are high values,corresponding to a state of drowsiness just before falling in a slumberwhoever the individual. Therefore, in the same way that the PERCLOS₈₀parameter makes it possible to define, when it is lower than 3%, in areliable way a fully alert state, the latter parameter, namedDURATION₅₀, allows when it reaches a level of 0.6 to detect in areliable way, a state of loss of alertness. The detection of these twoextreme values, enables to define other thresholds, by a learningmechanism, related to other parameters that are more sensitive toalertness but more individual dependent.

The AVR parameter is defined by the ratio of the eye blink peakamplitude (814) to the maximum eyelid closing speed (813). Thisparameter is assessed for each peak of spontaneous eye blink over agiven measurement time, e.g., 3 minutes.

FIG. 9A, by plotting the successive values (902) of this parameter withtime (901) for an alert individual, they line up substantially on astraight line (903). Starting from the dots cloud thus plot, adispersion interval (904) is estimated for the alert individual, 90% ofthe cloud being comprised in this interval. The slope of the line andthe width of the interval are individual dependent and for a sameindividual are likely to vary in time.

FIG. 9B, when the same individual, shows signs of reduced alertness, thevariance of the AVR parameter measured over the interpolation timeincreases, which translates into measurement dots lying outside theinterval calculated in the alert state for the same individual.

Thus, for instance, a scalar index of drowsiness/alertness is obtainedby counting the number of times the assessed AVR value is out of theinterval, over a given time, said interval boundaries being calculatedwhen the individual is in an awakened state.

The interval must be calculated for each individual. For example, theline (903) equation and the interval (904) are calculated from the mostrecent AVR values that were assessed when the individual was in aconfirmed awakened state, i.e., with a PERCLOS₈₀<3%, the correspondingdata are stored and updated in the memory means of the processing andcalculation unit.

Additional parameters derived from the accelerometer signal allows todetect and to characterize a head drop, its associated frequency orduration, these parameters being characteristic of an advanced drop ofalertness.

According to an exemplary implementation, only the accelerationaccording to the direction of gravity is used, that is to say accordingto they axis in the embodiment shown FIG. 2.

In normal circumstances, the accelerometer measures an acceleration of 1g directed according to the positive direction of the y axis andcorresponding to the gravity.

FIG. 10, on a diagram showing the variation of the acceleration on theyaxis (1002) vs time (1002), at the time of a significant drop ofalertness (1003, 1004) translating in a micro slumber, the head of theindividual falls forwards according to the neck joint of leastresistance.

In the extension position, with the head leaning forward, theorientation of they axis compared to gravity makes that the projectionof gravity acceleration on this axis is lower than 1 g, and then reaches1 g again if the individual straightens its head. Therefore, a head drop(1003, 1004) is detected if the acceleration according to the y axistakes a value that is less than a threshold value (1005).

The signal is initially filtered by a low pass filter, with a cut-offfrequency of about 2 Hz in order to remove from the signal the shakesrelated to the activity of the individual. Only a head drop lasting oversignificant duration is taken into account, e.g. lasting more than 0.2second. Thus, a scalar parameter is for example determined by the numberof head drop found over a given measurement time. A second scalarparameter corresponds to the number of head drop lasting more than asecond and longer duration threshold (1004), for example longer than 0.5or 1 second, counted over the same measurement time interval or a longertime interval.

These scalar parameters:

-   -   PERCLOS₈₀, ν₁(t);    -   DURATION₅₀, ν₂(t);    -   number of AVR points outside the forecast range, ν₃(t); and    -   number of head drops and long-lasting head drops, ν₄(t), ν₅(t).        where t is the time, are calculated in real time and are        combined into a composite index that reflects the state of        alertness of the individual and from which the decision to        generate an alarm is made.

The calculation principle of the composite index is similar whatever thetype of risky situation whose detection is aimed, but uses differentparameters depending on the type of detection sought.

A shown in the aforementioned example related to alertness assessment,the parameters considered for the composite index computation, combinesat least one parameter that is individual dependent such as ν₃(t) and atleast one parameter that is not dependent individual dependent, such asν₁(t), ν₂(t), ν₄(t), ν₅(t) either taken alone or in combination.

According to an exemplary embodiment and depending on the nature of thedetection sought, these parameters are whether scalar or binaries, inthe latter case taking the value 0 or 1 (or −1, +1) depending on whethera specific pattern is detected or not in the signal.

Accordingly, the parameters issued from the signals processing, whetherscalar or binaries, are functions of time and noted ν₁(t) . . .ν_(n)(t).

They are grouped in a M(t) vector:

${M(t)} = \begin{bmatrix}{v_{1}(t)} \\\vdots \\{v_{n}(t)}\end{bmatrix}$

A severity composite index V(t) related to a risky situation is, e.g.,defined as:V(t)=A·V(t−1)+B·M(t),where A and B are matrices of coefficients which are specific to theindividual and that are weighting the influence of each parameterrelative to one another.

According to a simple example of implementation, at the beginning (t₀):

${{V\left( t_{0} \right)} = {V_{0} + {B \cdot {M\left( t_{0} \right)}}}},{B = \begin{bmatrix}\beta_{11} & \cdots & \beta_{1n} \\\vdots & \ddots & \vdots \\\beta_{n\; 1} & \cdots & \beta_{nn}\end{bmatrix}},{A = \left\lbrack {\alpha_{1}\mspace{14mu}\ldots\mspace{14mu}\alpha_{n}} \right\rbrack},{{and}\mspace{14mu}{V(t)}\mspace{14mu}{is}\mspace{14mu} a\mspace{14mu}{{scalar}.}}$

The α_(i) and β_(ij) factors as well as the equation used for thecombination of the parameters for the calculation of the compositeindex, evolve with the machine learning process, notably by the datastatistical analysis performed at the server level (411, FIG. 4).

Based on the level of the composite index, several alarm levels aretriggered. Coming back to FIG. 2, a first level of alarm corresponding,e.g., to an early stage of alertness drop, leads to the light up of theled (282) either continuous or blinking. A second alarm levelcorresponding to a further loss of alertness, triggers the buzzer. Athird level activates simultaneously the led and the buzzer, and if thesystem is configured to do so, sends a message to the connected devicesin proximity with the connected object paired with the eyeglasses.

FIG. 11, according to an exemplary embodiment, the method of theinvention comprises a first step (1110) for checking out the actualwearing of the eyeglasses. This step aims at ensuring the consistency ofthe further processing carried out, but also to turn the eyeglasses intoa sleep mode if they are not used, in order to reduce the electricalconsumption.

This check-out step, uses only the signal issued by the IR receiverusing a specific filter and a specific processing. If the result of thecheck-out test (1115) is negative, the eyeglasses are turned (1116) in asleep mode.

While in sleep mode, a check out test is performed on a regular basis,for example every minute, in order to activate the active mode, if theeyeglasses are detected as worn by the user. If the eyeglasses aredetected as worn by the user, the signals acquisition (1120) islaunched, this acquisition includes filtering operations specific toeach signal. The acquisition is carried out at a sampling frequencyranging from 50 Hz to 150 Hz preferably around 70 Hz, who turns out tobe a frequency to collect enough data to make the appropriateprocessing, while limiting the electrical consumption.

The signals thus conditioned are sent to processing modules (1131, 1132,1133, 1134) which extract from said signals the specific andrepresentative parameters either scalar or binaries. Thus, according toan exemplary embodiment, one of the modules (1131) is dedicated to theextraction of the parameters derived from the signal issued by the IRreceiver. Another module (1132) is dedicated to the extraction of theparameters from the signals issued by the accelerometers, a third module(1133) is dedicated to the extraction of the parameters from the signalissued by the barometric sensor and a fourth module (1134) is dedicatedto the extraction of parameters from the impedance measurement of thecircuit comprising the electrodes.

The parameters resulting from this processing are combined in compositeindexes, during a calculation step also implementing several modules,for example, a module for the calculation of alertness (1141) using theparameters derived from the processing of the signal issued by the IRreceiver and at least one parameter resulting from the processing of thesignal issue by the accelerometer, a module of calculation (1142)relating to the falls using the parameters resulting from the processingof the accelerometry signals and, according to a specific embodiment,those derived from the processing of the signal issued by the barometricsensor, a module of calculation (1143) relating to the falls known assoft, using parameters resulting from the processing of accelerometryand barometric sensor signals, a module of calculation (1144) relatingto the recovery after a fall, using the parameters resulting from theprocessing of the accelerometry signals, the IR receiver signal and thesignal from the barometric sensor, and a module (1145) combining theinformation derived from the IR sensor and the impedance measurementinvolving the electrodes for assessing dehydration.

Each module of calculation thus defines a composite index relating tothe risky situation whose detection is aimed. Each of these compositeindexes is compared to a threshold value that is stored in memory, thatis to say an alertness test (1151), a fall test (1152), a soft fall test(1153), a recovery after fall test (1154) and a dehydration test (1155).

If the threshold value is passed an alarm request is addressed to analarm management module (1161, 1162, 1163). According to this example,three alarm management modules are used. An alarm management module(1161) relating to alertness, that triggers an alertness alarm accordingto an alertness composite index as described above. An alarm managementmodule (1162) relating to falls, which depending on the passing of athreshold pattern of the 3 composite indexes related to falls, triggersvarious means of alarm, considering all or part of the composite indexesof fall, soft fall, and recovery after fall, and an alarm managementmodule (1163) related to dehydration.

If no threshold is passed, the acquisition and processing of the signalscontinue without change until a possible detection of an alarmcondition. Therefore, starting from a common acquisition basis, carriedout with a limited number of sensors and of processing modules (1131,1132, 1133, 1134), the functionalities of the system are adapted to theneeds by activating or loading the specific calculation and alarmmanagement modules.

As for instance, if the user of system of the invention is young,healthy and not working in a dangerous environment, the main targetedfeatures are alertness monitoring, for example when driving anddehydration. In such a case, the modules relating to the calculation andthe alarm management relating to falls (1142, 1143, 1144, 1152, 1153,1154, 1162) are not activated, although the information derived from theaccelerometers remains used, in particular for the detection of a headdrop. To the opposite, for an older person, not driving, the main risksto be covered are that of the fall and a dehydration. In such a case thealarm management modules relating to alertness (1141, 1151, 1161) arenot activated, which however does not mean that information resultingfrom the IR receiver is not used, they are indeed used in thecalculation module (1144) dealing with the recovery after fall, and alsofor dehydration measurement. Finally, for other specific cases, all themodules are activated.

FIG. 12, signals from the IR receiver are used to check out if the useractually wears the glasses.

FIG. 12A, when following the evolution of the intensity (1202) of thesignal emitted by the IR receiver according to time (1201) duringsuccessive putting and withdrawal of the eyeglasses, when the glassesare removed (1204, 1206), the emitted infra-red beam is not reflected bythe eyelid or the cornea and the signal intensity is low. On the otherhand, as soon as the glasses are correctly worn (1203, 1205, 1207) bythe user the reflection of the signal on the ocular area clearlyincreases the intensity of the signal.

FIG. 12B, according to an exemplary embodiment, in order to detect ifthe user is wearing or not the eyeglasses, the signal issued from the IRreceiver is strongly smoothed (1211) for example by means of anexponential weighting moving average filter.

Using the time derivative (1212) of the filtered signal makes itpossible to easily detect an event of taking off (1214) or putting on(1213) of the eyeglasses.

Alternatively, or in a complementary way, a threshold (1220) is definedso that the glasses are correctly worn by the user when the intensity ofthe signal (1211) thus strongly filtered, takes values higher than thisthreshold (1220). When the user does not wear the eyeglasses, forinstance because they fell down following a fall, or when it does notwear them correctly, for example too ahead on the nose or when they donot rest on the two ears, the calculation of parameters, not only thoseissued from the IR receiver signal but also derived from the signalsissued by the other sensors is erroneous.

Therefore, the actuation of the sleep mode following the detection ofthe user not wearing or not properly wearing the eyeglasses isprogressive and starts with the emission of a specific alarm, e.g., onthe led and the buzzer and possibly on the connected object paired withthe glasses. Then, during the periodic tests performed in the sleepmode, a short alarm is triggered if the glasses are still detected asnot worn or incorrectly worn by the user, for example by a brief andsimultaneous triggering of the led and the buzzer, for each testperformed, e.g., within 15 minutes after the actuation of the sleepmode. Beyond this period, the system shifts to a deeper sleep mode whereno alarm is triggered

FIG. 13, for the detection of simple falls, the calculation of relevantparameters uses the accelerometer signals. The signals are initiallyfiltered through a low pass filter with a low cut-off frequency, e.g.,0.1 Hz, in order to eliminate vibrations and phenomena corresponding toeveryday life activities. According to an exemplary embodiment, a secondfiltering such as a moving median filter, preferentially of 3^(rd)order, is performed, this type of filter makes it possible to eliminatethe random noise while preserving the peaks acuity. FIG. 13A, takinginto account the positioning of the accelerometer, the gravity beingdirected according to the positive y axis, a first major effect of afall is detected by a drop of the acceleration measured according to they axis which is also detected on the sum of accelerations according tothe three axes.

Thus, by plotting the evolution of the sum of accelerations (1302)according to the 3 axes of the accelerometer vs time (1301), a fallevent is characterized by the appearance of a first peak (1303) directedin the negative direction and corresponding to the free fall phenomenon.That first peak is almost immediately followed by a second peak (1304)directed in the positive direction of the axis (1302) and correspondingto the impact of the body on the ground or on any other obstacle.

Therefore, the appearance of two consecutive inverted peaks in the sumof accelerations, in a given time window, each exceeding a threshold(1305, 1306), is a specific pattern indicative of a fall. As a forinstance, the lower threshold value is set at 0.6 g (5.89 m·s⁻²) and theupper threshold (1306), corresponding to the impact, is set at 2 g(19.62 m·s⁻²).

These values are not user dependent and lead to a parameter of thebinary type, translating whether or not such a pattern is detected overa given measurement time. With these threshold values, everyday lifeactivities such as walking or stepping down a stairway do not generate adetectable pattern and thus do not generate any false alarm.

FIG. 13B shows evolution (1312) of the time derivative of the signalissued by the barometric sensor vs time during a fall event followed bya recovery where the person raises up again. A first peak (1313)corresponds to the fall, i.e., an altitude drop resulting in an increasein the measured atmospheric pressure.

The individual then remains on the ground for a certain time, thus thepressure stabilizes, then it raises up, which corresponds to a secondpeak (1314) of reduction of the pressure or increase in altitude.

These events occur over a longer time than the succession ofacceleration peaks observed during a fall event. Therefore, a fall eventis also characterized by a binary parameter, corresponding to theappearance of a positive peak (1313) in the time derivative of thebarometric pressure whose amplitude exceeds a certain threshold

A three feet (1 meter) free fall implies a pressure variation of 12 Paover a duration of approximately 0.3 seconds. Actually, a fall is rarelycompletely free so that the threshold is for example set between 10Pa·s⁻¹ and 20 Pa·s⁻¹. The corresponding characterization parameter is abinary parameter whose value depends on whether or not such a positivepeak is observed over a given measurement time. The recovery after thefall can be detected by the appearance of a second peak (1314) invertedwhen compared to the first and which amplitude exceeds a thresholdvalue, for example comprised between 5 Pa·s⁻¹ and 10 Pa·s⁻¹.

So, an additional parameter for the characterization of a fall is abinary parameter, indicating the presence of a recovery peak on the timederivative of the pressure signal in a given interval of time followingthe fall peak. Finally, an additional parameter, of scalar type,corresponding to the time (1317) separating the fall peak (1313) fromthe recovery peak (1314) on the time derivative of the pressure signalis also used to characterize the seriousness of a fall.

These parameters are combined into a composite index according to asimilar principle to the one exposed for the measurement and detectionof the loss of alertness, which composite index is used to triggerdifferent levels of alarm.

The method exposed above is effective for detecting a fall involvingfree fall phenomenon, even of a short duration found in the case of anaccidental fall or in the case of a sudden loss of consciousness.

However, in certain circumstances or for some people at risk, the fallcan be caused, for example, by a progressive loss of consciousness,leading to a fall, known as a soft fall, not allowing to detect a freefall phenomenon. However, this type of fall is critical for some peopleat risk. If a free fall event can be detected by the peak (1303)directed according to the negative y axis, such a peak is not generallyseen in the case of a soft fall, the peak of impact (1304) is howeverdetected, although with a lower amplitude than in the case of anaccidental fall.

The same applies for the signal corresponding to the time derivative ofthe barometric pressure, a peak (1313) corresponding to the altitudedrop is well observed but less salient in case of a soft fall.Therefore, a soft fall is characterized by the appearance of an impactpeak, detected on the sum of accelerations, with a lower threshold ascompared to the case of a free fall, and by a positive peak in the timederivative of the pressure signal, also detected considering a lowerthreshold value. These two parameters are binary parameters reflectingthe appearance of such peaks in the measurement interval.

However, using only these two parameters with lowered thresholds leadsto a risk of detecting a negative false, i.e., to interpret as a fall asituation of the everyday life, like sitting down on a chair or in anarmchair.

FIG. 14, to the difference of an everyday life situation like sittingdown in an armchair, a fall, even a soft fall, implies a loss ofverticality. The position of the glasses, on the head of the individual,is particularly advantageous to measure such a loss of verticality. Theloss of verticality is measured for example by the value of theresulting acceleration in a plane perpendicular to the gravity, that isto say on the x and z axes while referring to FIG. 2. Thus, the plot ofthe intensity of acceleration (1402) in a plane perpendicular to thegravity vs time (1401) during a soft fall event, clearly reveals one ormore peaks (1403) higher than a threshold (1404) which are thusdetectable and whose detection over the acquisition time is captured ina binary parameter. These various parameters are combined in a compositeindex in order to detect a soft fall and to generate an alarm.

However, the combination of these parameters still does not make itpossible to detect and characterize a soft fall during which the headremains appreciably vertical, as it is the case for a fall whereas thesubject is leaned against a wall, or of another complex situation,leading to a negative or a positive false.

In order to cure these deficiencies, the complete algorithm for thedetection and the characterization of the falls takes into accountparameters determined in the moments following the fall and whichgenerally attests of the recovery, or not, of the victim. Theseparameters allow, among other things, to reduce the rate of negativesfalse, more specifically in case of soft fall, by avoiding thegeneration of alarms and the notifying of rescue services in situationsthat are not justified.

As for instance, in addition to the time separating the fall from apotential recovery as defined in FIG. 13, a serious soft falltranslates, for example, by a loss of consciousness of the individual.Such a loss of consciousness can be captured, in particular, by:

-   -   the individual remains staying in a nonconventional posture;    -   the individual does not exhibit a significant activity; and    -   the eyelid activity of the individual corresponds to a serious        loss of alertness.

The posture of the individual can be determined for example by thevalues of the acceleration on the different axes of the accelerometer.When the person is motionless or quasi motionless the accelerometer isonly subjected to the action of the gravity, which projects according tothe positive y axis of FIG. 2 when the head is straight. Therefore, bymeasuring the acceleration components according to the 3 axes of theaccelerometer, the orientation of the head is given. This orientation isdefined by an angle compared to the theoretical vertical position of thehead. The value of this angle is a scalar parameter, symptomatic of theposture of the individual after a fall.

The activity of the individual after a fall is also measured consideringthe signal issued by the accelerometer. If the individual moves,acceleration variations are observed. Therefore, the variation magnitudeof the accelerations over a given time frame, measured for example bythe variance of the acceleration signal over this time frame, is asymptomatic scalar parameter of the activity of the individual.

The measurement of the eyelid activity and the parameters which arededuced from it has been presented above.

Of course, the calculation of the activity parameters following a fallis not limited to the case of a soft fall but is also relevant in theevent of an accidental fall.

The various parameters are combined in a composite index, according tothe method exposed previously, the level of which is used to decide ofthe triggering of alarms.

In a specific but not exceptional case, the eyeglasses fall down fromthe head of the individual upon the fall or stay in an incorrectposition on its face during a time following the fall. In such a case,even if a fall signature can be detected, the parameters characterizingthe fall by the behavior of the individual in the moments following thefall are not measurable or are measured in an erroneous way.

Thus, according to an exemplary implementation, following the detectionof a fall, the generation of an alarm based on the parameters assessedafter the fall event comprises a check out of the correct wearing of theeyeglasses by the individual. If a not wearing or an incorrect wearingis detected, an alarm is generated and repeated during a defined time,as long as the glasses are not put on correctly. If after this definedtime, in spite of the emission of the alarms, the eyeglasses are stillnot correctly worn, then it is possible that the person is not able toput them on back, and an alarm is triggered.

The dehydration state of an individual is given by the water content ofthe body of the person as a percentage of its weight, or Total BodyWater (TBW).

When the assessed TBW crosses a predetermined threshold that is afunction of the individual, the system generates an alarm indicatingthat the person has reached critical conditions in terms of dehydration.

The IR transmitter and the IR receiver may be used to measure the IRlight absorption of the blood conveyed by the blood vessels in the eye,either under the sclera or in the eyelid. The pattern of absorption ofIR light by the blood can be correlated to the hydration state of theperson.

To this end, the emission power of the IR receiver is increased atregular time intervals, as for instance, every 10 minutes, in order tomeasure the IR absorption pattern of the blood and assess the hydrationstate of the person.

The reflectance of the eye is also a function of the hydration of theeye, which in turn is an indicator of the hydration state of the person.This reflectance is also measured by means of the IR transmitter and theIR receiver.

These parameters: IR absorption pattern of the blood and reflectancechange from one person to another, therefore these parameters areindividual dependent and a calibration is required for thesemeasurements.

The impedance variation of the skin with hydration when the electrodesare supplied with a low voltage and high frequency alternative currentresults from resistance and capacitance variations of the skin with thehydration level. The impedance measurement is in the range of a fewhundreds of ohms, e.gs. 200 to 500 ohms.

The impedance of the skin value corresponding to a well hydrated subjectis dependent upon the voltage and the frequency of the current, but isweakly dependent on the individual. Therefore, a threshold may bedefined, that is independent of the user and stored in the memory meansof the device.

In an alternative embodiment, impedance measurement may be performed atvarious frequencies. Capacitance variation are more sensitive in thelower frequency range, i.e., in the kHz range, while resistivityinfluences the results in the 10 kHz range.

These two frequencies measurement may be performed either sequentiallyby the same set of electrodes or by two different sets of electrodes.

A drop of about 10% from the nominal value of the impedance thusmeasured, indicates a dehydration state.

Such measurement may be performed on regular time intervals, e.g. every30 minutes.

The device and the methods specified above allow to address most of therisky situations a person, more particularly an elderly, may face.

The same set of sensors or part thereof may also be used in order todetect a more general fall prone situation without connectingspecifically this situation to a loss of alertness or to a dehydrationstate.

The inventors found that such a fall prone situation may be correlated,when referring to an individual, with the evolution of parameterscharacterizing:

-   -   a walking pace;    -   a sit to stand, or STS, condition; and    -   a head posture.

More particularly parameters like:

-   -   a step duration variability;    -   a head posture while walking;    -   a daily number of STS;    -   a duration of a STS; and    -   a STS peak acceleration along a gravity axis.        may be taken alone or in combination in order to compute one or        more composite indexes characterizing a fall prone situation.

From an overall point of view, those parameters may also be used as ameasure of the muscle tone of an individual and may be combined in oneor more composite indexes characterizing the muscle tone of anindividual wearing the eyeglasses, without departing from the invention.

All of these parameters may be computed from the signal issued by thetriaxial accelerometer alone. Adding the information issued by a gyrosensor simplifies the computation of relevant parameters, and adding thebarometric sensor improves the accuracy of STS detection andcharacterization.

In an exemplary embodiment the method of the invention computes 7parameters and combine them in a composite index.

FIG. 16, a first parameter for a fall prone situation detection is basedon a variance of a walking step duration. To this end, the signal issuedby the triaxial accelerometer is filtered by a low pass filter in orderto limit the influence of events that are not related to the walk. As anonlimiting example the a cut off frequency of the low pass filter isset to 4 Hz or under.

When looking at the amplitude of the acceleration (1602) along thegravity axis with time (1601) while the individual is walking, each timea foot hits the ground corresponds to a peak (1611 ₁ . . . 1611 ₈)exceeding a certain threshold (1603), e.g., 10 m/s². The time (1610 ₁ .. . 1610 ₇) separating two such consecutive peaks gives the duration ofa step.

Looking to FIG. 2, the gravity direction is given by the y axis when theeyeglasses wearer is looking straight ahead. When the wearer head isleaning towards the front or towards the side, as shown hereafter, thedirection of gravity will exhibit projected components on the x and zaxes. Therefore, the component of the acceleration on the gravitydirection, as considered in FIG. 16, is computed by the accelerationmeasured over the 3 axes of the triaxial accelerometer and using thehead posture information, either derived from the signal of theaccelerometer itself or using the information issued by a gyro sensorwhen the MEMS comprising the accelerometer includes such a sensor.

The triaxial accelerometer or the inertial MEMS are thus used as apedometer. The computed filtered signal projected on the gravity axis isfurther designed as the “pedometer signal” (1605).

A first parameter is assessed by computing the step duration varianceover a given number of consecutive steps.

To this end, once a peak (1611 ₁) crossing the acceleration threshold(1603) is detected on the pedometer signal (1605), said pedometer signalis scanned and recorded over a given duration or assessment time, calleda walking sequence, and the number of consecutive peaks (1611 ₂ . . .1611 ₃) is counted over this duration as well as the time (1610 ₁ . . .1610 ₇) separating each peak.

The duration of the walking sequence in which the walking cadence isassessed may be set, as for instance, between 6 seconds and 15 secondsdepending on the age and gender of the wearer, the older the longer.

The record is considered as valid provided that:

-   -   the walking sequence comprises a minimum of consecutive peaks,        e.g., 10 peaks, and    -   the time separating any two consecutive peaks in the assessed        walking sequence is lower than a predetermined value set        depending on age and gender of the eyeglass wearer, typically        between 900 ms and 1800 ms, the older the longer.

As an exemplary embodiment, provided that the sample walking sequence isvalid, the variance of the time (1610 ₁ . . . 1610 ₇) separating 2consecutive steps is computed over the sample and stored in the memorymeans of the eyeglasses along with the date (day and time) of themeasurement. In a variant embodiment, the walking cadence, i.e., thenumber of steps over the walking sequence is also recorded, e.g. thenumber of steps per minute.

When the pair of eyeglasses is paired with a connected object asdescribed above, the information may also be stored in the connectedobject memory means for archival purpose or to be anonymouslytransmitted to a server for further analysis either by the connectedobject or by remote means.

Such records may further be used to provide an indicator of the shape ofan individual: a healthy individual walks at least a certain time a day,depending on its age, at a regular minimum pace, like 100 steps perminute, also depending on its age and gender. These indicators give anassessment of the shape of the individual, based on average populationfigures, while the analysis of the step duration variance and itsevolution are more individual oriented.

FIG. 17, in an exemplary embodiment, a second relevant parameter for afall prone situation detection, is found to be the variation of the headposture during a walking sequence.

An individual will be more prone to a fall and will exhibit a lowermuscular tone if its head is falling, chin to chest, during a walkingsequence.

The position of the head of the individual during a walking sequence maybe assessed using the information issued by the triaxial accelerometeritself, which according to the components of the acceleration over the 3axes may be used to evaluate the orientation angle of the head (1702),more particularly its angle around the z axis of FIG. 2.

Alternatively or in combination, the head orientation of the individualmay be assessed with the gyro sensor if the triaxial accelerometer iscoupled with such a sensor in an inertial MEMS.

Looking at the variation of this head angle (1702) with time (1701)during a walking sequence allows to compute an additional parameter fora fall prone detection analysis. As a for instance, at the beginning(1712) of the walking sequence, the individual wearing the eyeglasses islooking straight ahead.

During the walking sequence the head posture progressively changes, thehead falling front wise, the chin falling closer to the chest, to reacha final position (1713), where the head is clearly leaning.

As an exemplary embodiment a second parameter is defined as a ratio ofthe time (1711) during which the head of the wearer is leaning forwardover a certain threshold angle (1703) by the duration (1710) of a validwalking sequence. The threshold (1703) is defined relative to an averageposture (1705) of the wearer that may be set during a calibrationprocess of the eyeglasses. The valid walking sequence duration (1710) isdefined in the same way as detailed for the walking pace parameterassessment.

The parameter is recorded in the memory means of the eyeglasses alongwith the date. Additionally, when the eyeglasses are paired with aconnected object, the information may also be recorded in the memorymeans of the connected object for archival or to be anonymouslytransmitted to a server for further analysis either by the connectedobject or by remote means.

In addition to this first set of parameters based on the analysis of awalking sequence, a second set of parameters is computed, based on theanalysis of sit to stand movements of the individual wearing theeyeglasses.

FIG. 18, a sit to stand movement may be detected by processing thetriaxial accelerometer signals and considering the acceleration alongthe gravity axis.

A sit to stand, or STS event, is detected in the signal (1805) by aspecific pattern (1811, 1812) when looking at the acceleration (1802)with time (1801), namely a peak up followed by a peak down.

In an exemplary embodiment, such pattern (1811, 1812) is taken intoaccount if both peaks exceed or cross given thresholds (1803, 1804)which are set according to the individual and more specificallyaccording to its age, said threshold crossings being observed in amaximum given time which is also set according to the age of theindividual wearing the eyeglasses.

As a nonlimiting example, the thresholds (1803, 1804) on theacceleration peaks are set to +/−5 m/s² and the maximum time separatingthe crossing of these thresholds (1803, 1804) is set to 500 ms.

In addition, the signal issued by the barometric sensor may also betaken into account in order to detect a valid STS pattern.

Each detected STS is recorded with its date (day and time) in the memorymeans of the eyeglasses and additionally in the memory means of aconnected object, if the eyeglasses are paired with such an object,along with parameters characterizing the STS event:

-   -   the duration (1821, 1822) of the STS event; and    -   the peak acceleration (1831, 1832) reached during the STS event.

From these records further parameters are computed, namely:

-   -   the daily number of STS events;    -   the day-to-day variation of the daily number of STS events;    -   the mean duration of STS events over a day; and    -   the standard deviation of the STS events duration.

A composite index is computed, as explained earlier, with the five abovecited parameters and the 2 parameters derived from the walking sequencesanalysis, namely:

-   -   the variance of the steps duration; and    -   the head posture variation.

Such a composite index is compared to specific threshold values adaptedto the age, the gender, the physical condition and the risk level of theindividual.

According to an advantageous embodiment, the threshold values are alsodefined according to the time of the day, i.e., morning, afternoon,evening.

When the composite index crosses a threshold value, an alarm isgenerated. The alarm may be issued on the means of the eyeglasses butmay also be sent to a caretaker or a relative of the individual wearingthe eyeglasses.

Before being used effectively, the eyeglasses of the system must beadapted to their user.

This adaptation comprises a mechanical adaptation, in particular of thestems, and a calibration of the sensors, more particularly of theaccelerometer and of the IR receiver.

The calibration is carried out by a professional, for example anoptician, or by the user himself, guided by an application set up in thesmartphone connected to the glasses.

The accelerometer calibration aims to determine accurately the gain oneach of the axes and the rotation matrix so that the acceleration of thegravity is oriented according to the y axis when the user wears theglasses in a way considered to correspond to a vertical position of thehead.

According to an exemplary embodiment, this calibration is performedusing 3 acquisitions done in defined configurations. According to afirst configuration, the eyeglasses are placed perfectly horizontal, ina position corresponding to the wearing position, for example in abracket that is specially adapted for this purpose. In such acircumstance the y axis is supposed to measure a positive 1 gacceleration.

According to a second configuration, the eyeglasses are placed perfectlyhorizontal, in a position that is reversed from the wearing position,for example in a specific bracket. In such a circumstance they axis issupposed to measure a negative 1 g acceleration. In a specificembodiment the brackets used for these operations are part of theeyeglasses packaging.

In a third configuration the glasses are worn by their user in a righthead position. The analysis of the three measurements carried out underthese conditions makes it possible to caliber the accelerometer.

The calibration of the IR receiver consists in particular to set thethreshold that allows to discriminate voluntary eye blinks fromspontaneous eye blinks. According to an exemplary calibration method,the user wears the eyeglasses for a fixed period, e.g., 1 minute, duringwhich it performs successive voluntary eye blinks at defined timeintervals, e.g., every 10 seconds. During the acquisition phase, thesystem adjusts its setting, in order to detect 6 voluntary eye blinkpeaks and from 10 to 20 peaks of spontaneous eye blinks. The method maybe repeated several times in order to check out the correct adjustment.

For calibrating the IR couples with regard to dehydration measurements,the subject must be well hydrated, which can be checked by using theimpedance value. The emission power of the IR transmitter shall be setfor both the measurement on the sclera and on the eyelid, as well as thelevel detected on the IR receiver.

These calibration operations are advantageously carried on a periodicbasis.

FIG. 15, according to a specific embodiment, the eyeglasses of thesystem of the invention comprise additional sensors. This enhancedversion allows to detect other risky situations. This paragraph and FIG.15, only quote the sensors not previously described. As an exemplaryembodiment the enhanced version comprises:

-   -   a thermometer (1501) to measure the body temperature; and    -   a heart pace sensor (1502).

These two sensors are advantageously placed on the stem ear pieces,behind the ears, for more reliable measurements:

-   -   a microphone (1503);    -   a blood pressure sensor (1504), coming in contact with the        temple of the user;    -   the heart pace sensor (1502) is advantageously equipped with a        photodiode to measure the blood oximetry; and    -   a blood glucose sensor (1505), for example, an infra-red sensor        measuring the glucose level in the blood through the skin.

The description above and the exemplary embodiments show that theinvention achieves its goal, namely to propose a customized system formonitoring the occurrence of a risky situation, using a discrete andaesthetic sensor.

The invention claimed is:
 1. A method for preventing and detecting afall of a user and implementing a system comprising: a pair ofeyeglasses with hinged stems including rims for supporting glasses, wornby the user and comprising a plurality of sensors and an alarm, theplurality of sensors being set in the hinged stems and the rims of theeyeglasses, wherein the plurality of sensors comprising: a triaxialaccelerometer; an infrared (IR) transmitter and an IR receiver ofinfrared light both directed to a cornea of the user; a barometricsensor; wherein each of the triaxial accelerometer, the IR transmitterand IR receiver, and the barometric sensor of the plurality of sensorsgenerates a different signal, and is connected to a microprocessorconfigured to execute a computer program stored in a memory to collectand analyze data issued by the plurality of sensors, and to trigger thealarm in response to an analysis of the data; wherein the triaxialaccelerometer generates a first signal that is acquired and processed toderive a walking pace parameter, a sit to stand parameter, a headposture parameter and an acceleration magnitude over three axes of thetriaxial accelerometer; the method comprising: computing a firstcomposite index based on the walking pace parameter, the sit to standparameter and the head posture parameter; and generating a first type ofalarm in response to a determination that the first composite indexexceeds a predetermined threshold; acquiring a second signal of thebarometric sensor; computing a second composite index based on: theacceleration magnitude combined along the three axes of the triaxialaccelerometer; a variance of the acceleration magnitude over apredetermined duration; an acceleration component over an axis of thethree axes of the triaxial accelerometer parallel to gravity; theacceleration magnitude combined over the three axes of the triaxialaccelerometer in a plane perpendicular to the gravity; and a variationof a barometric pressure between two moments; generating a second typeof alarm corresponding to the detection of the fall of the user inresponse to a determination that the second composite index exceeds thepredetermined threshold; controlling the IR transmitter; collecting andprocessing a third signal from the IR receiver to detect a closure andan opening of an eyelid of the user; computing an alertness compositeindex based on the opening and closure of the eyelid of the user; inresponse to the generation of the second type of alarm, computing athird composite index based on a body posture parameter derived from thehead posture parameter and the barometric sensor, and the alertnesscomposite index; and generating a third type of alarm in response to adetermination that the third composite index exceeds the predeterminedthreshold.
 2. The method of claim 1, further comprising determining thatthe eyeglasses are worn by the user by performing a check out test thatcomprises activating the IR transmitter and analyzing the third signalof the IR receiver in response thereto.
 3. The method of claim 1,wherein said computing the first composite index based on the walkingpace parameter, the sit to stand parameter and the head postureparameter comprises: projecting the first signal issued by the triaxialaccelerometer on the axis of the three axes of the triaxialaccelerometer parallel to a direction of the gravity to obtain apedometer signal; obtaining a threshold value and detecting consecutivepeaks in the pedometer signal exceeding the predetermined threshold,during a predetermined assessment time; measuring a separation timeseparating two consecutive peaks of the consecutive peaks during thepredetermined assessment time; computing a variance of the separationtime over the predetermined assessment time; and utilizing the varianceof the separation time over the predetermined assessment time incomputing the first composite index.
 4. The method of claim 3, furthercomprising: assessing an angle of a variation of the head postureparameter of the user during the predetermined assessment time;obtaining a threshold angle and measuring a time the angle of thevariation of the head posture parameter of the user during thepredetermined assessment time exceeds the threshold angle; and utilizingthe time the angle of the variation of the head posture parameter of theuser during the predetermined assessment time exceeds the thresholdangle in computing the first composite index.
 5. The method of claim 4,further comprising: detecting a sit to stand event by a predeterminedpattern in the first signal issued by the triaxial accelerometer on theaxis of the three axes of the triaxial accelerometer comprising anacceleration parallel to the direction of the gravity; measuring aduration of the sit to stand event; measuring a peak acceleration duringthe sit to stand event; and utilizing the duration of the sit to standevent and the peak acceleration during the sit to stand event incomputing the first composite index.
 6. The method of claim 5, furthercomprising: counting a number of sit to stand events per day; andutilizing the number of the sit to stand events per day in computing thefirst composite index.